Why were Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius called the Five Great Emperors?

These 5 Emperors were an important group of these kindhearted leaders, who demonstrated restraint and justice in their actions, and were extraordinarily just. They chose successors who they thought would follow by/after their example, and they soon became called the Five Great Emperors.

They were called the Five Great Emperors because the way they'd rule as rulers demonstrated their own uniqueness in their actions such as, the showing of justice, the belief of peace, and restraint. The way they got noticed for this was because of their first actions, peace and prosperity.